Closing and injection valve especially for hot gas defrosting in freezing and cooling installations

ABSTRACT

A valve for closing a main fluid flow through a main flow passage having a valve stem with a valve head for engaging a valve seat to close the passage, the valve stem carrying at the end remote from the valve head a piston which can be actuated by a closing fluid against spring action to move the valve head (48) into closed position, the valve stem being hollow and is open at the valve head end and at the opposite end has openings opening into the interior of the hollow valve stem, and the piston is mounted for axial movement on the valve stem to allow further movement towards the valve seat against spring action when the valve head has engaged the valve seat and the valve stem has come to a halt, said further movement relative to the valve stem opening a passage into the openings in the valve stem, whereby closing fluid will be injected into the main flow passage at one side of the valve seat through the valve stem.

The invention relates to a valve for shutting off or closing a mainfluid flow through a main flow passage, comprising a valve stem having avalve head which may be operated to engage a valve seat in order toclose said passage, the valve stem carrying at the end remote from thevalve head a piston which operates in a cylinder and can be actuated bya closing fluid against spring action in order to move the valve stemand the valve head into closed position.

The valve according to the invention is especially designed for hot gasdefrosting in freezing or cooling installations comprising a compressor,a condenser and an evaporator of the dry or filled type.

The compressor, which may be of the piston, worm, lamella or turbo type,draws the vapourous cooling agent from the evaporator and therebymaintains a low pressure therein. In the compressor the gas iscompressed to the pressure determined by the operating condition of thecondenser. Through the compression an amount of heat corresponding tothe compression work is supplied to the vapour. This amount of heattogether with that supplied in the evaporator is removed by heatexchange in the condenser, in which the cooling agent is condensed to aliquid. The liquid is then passed to a suitable throttling means inwhich the pressure is reduced to the pressure in the evaporator. By thereduction of the pressure a small amount of the liquid will evaporate,so that the remainder of the liquid reaches the evaporation temperaturein operating condition. In filled evaporators liquid and gas will beseparated in a liquid separator. The liberated amount of vapour from thepressure reaction is withdrawn to the compressor together with theamount of vapour formed by the supply of heat to the evaporator. Therebythe circuit is completed.

A filled evaporator system in general consists of a liquid separatorassociated with one or more evaporator sections. The liquid from theliquid separator is made to circulate either by automatic circulation orby forced circulation. In the case of a forced circulation it ispossible to circulate far more liquid through the system (for instance 4to 6 times more) than in the case of automatic circulation. Theoperating liquid head and the pressure losses in the system are clearlyrelated, and especially an automatic circulation system must thereforebe designed in such a manner that the pressure losses in the supplypipes and liquid passages are small.

A dry evaporator system has no liquid separator, and the pressure isreduced in the inlet to the evaporator by means of a suitable throttlingmeans, usually a thermostatic expansion valve. The vapour leaves theoutlet from the evaporator in dry-saturated or overheated condition.

Defrosting of the evaporator sections is necessary in case white frostand/or ice is formed on the outer surfaces of the evaporator because ofthe purpose and the operating condition of the installation. This willusually be an undesirable effect, but it can be utilized for theproduction of ice. For defrosting the evaporator sections hot gas may beused, which is supplied from the pressure side of the compressor or froma reservoir.

In principle a hot gas defrosting is performed by shutting off theentire evaporator system or parts thereof and supplying hot gas on theevaporator side of the closing point. This hot gas will largely condensein the interior of the passages in the evaporator, and the evaporatormust be suitably drained, either to a suction accumulator, a returnconduit or a liquid separator or to the remaining evaporator system. Asuitable regulating system maintains the pressure in the defrostingsection at the level providing an effective defrosting and drainage.When the defrosting is completed, the supply of hot gas should cease andthe flow of cooling agent be resumed. The supply of hot gas can bedesignated as an injection, and as will appear from the precedingdescription it is to be effected on the evaporator side of the closingpoint and in the opposite direction of the closed cooling agent flow.

Known closing valves such as pilot controlled shut-off valves requirethe use of separate control devices for opening and closing the valve. Afurther valve is used to supply the injection fluid. Suitable directlycontrolled solenoid valves giving a sufficiently low pressure loss areonly available for relatively small dimensions. Commercial valves alsohave a comparatively high flow resistance in open condition because ofrestrictions in the flow passage, and they have a complicated structure.

Actuator controlled ball valves constitute an exception, but require theavailability of compressed air or hydraulic medium. Also, pilot valvesare required to provide the control functions. Electrically controlledactuators are often unreasonably expensive, but otherwise provide a goodalternative. However, leakages in the stuffing box of the ball valveoften make such actuators unsuitable for use in cooling installations.

The object of the invention is to provide an improved valve of the typereferred to initially, while at the same time combining the closing andthe injection functions in a simple manner. The valve according to theinvention is characterized in that the valve stem is hollow and at theend at which the valve head is provided, is open and at the opposite endhas openings opening into the interior of the hollow valve stem, andthat the piston is mounted for axial movement on the valve stem forfurther movement towards the valve seat against spring action when thevalve head has engaged the valve seat and the valve stem has thereforecome to a halt, said further movement relative to the valve stem openinga passage into the openings in the valve stem, whereby closing fluidwill be injected into the main flow passage at one side of the valveseat through the valve stem.

Accordingly, the valve according to the invention uses the injectionfluid as a medium which provides the closing of the main fluid flow. Atthe same time the design of the valve is such as to provide a lowpressure loss in open position.

The function of the valve depends on a correctly balanced relationshipbetween the pressure of the injection fluid and the available volumetricflow on one hand and the volume of the recipient (the evaporator) on theother hand, and on the pressure on both sides of the valve.

The valve will maintain a certain pressure difference between thepressure of the injection medium and thereby the recipient (theevaporator) on one hand and the pressure in the main flow passage on theother hand.

In operation of the valve according to the invention the medium to beinjected (the hot gas) is thus supplied to the distal side of thepiston, whereby piston and valve stem are advanced until the valve headshuts off the main flow. The moment the valve head engages the valveseat the movement of the valve stem is halted. However, the pistoncontinues and thereby opens passages for the supply of injection fluidthrough the piston rod (valve stem).

The valve according to the invention has a substantially simplerstructure than valves according to the state of the art, and at the sametime the control function is substantially simplified. The valve isfurther easy to assemble and disassemble. The valve can easily beprovided with a simple and substantially unobstructed passage in openposition so that the pressure loss is low. The valve can be reopened byshutting off the injection fluid, whereupon the pressure is equalized bya mechanical throttling element or a controlled equalization through avalve.

When the valve is used for hot gas defrosting in freezing or coolinginstallations as indicated above, the main flow passage of the valve isconnected into a return flow passage from the evaporator to a liquidseparator, and the closing and injection fluid is periodically suppliedfrom the pressure side of the compressor.

Further objects, features and advantages of the present invention willbe apparent from the subsequent description, reference being had to thedrawing.

FIG. 1 is an example of a schematic flow diagram for a coolinginstallation containing a valve according to the invention.

FIG. 2 is an axial section through the valve in open position.

FIG. 3 is a corresponding section through the valve at the moment thevalve head engages the valve seat, but before the passages for supplyingthe closing fluid have been opened.

FIG. 4 is a fractional view of the valve according to FIGS. 2 and 3after the piston has been displaced on the valve stem in order to openthe passages for the closing fluid.

In FIG. 1 a simplified cooling installation is shown schematically, saidinstallation comprising an evaporator 1, a liquid separator 2, acompressor 3 and a condenser 4. Between the condenser 4 and the liquidseparator 2 there is connected a throttle means 5, for instance in theform of a hand operated expansion valve. 6 is a control means in theform of a solenoid valve for the throttle means 5. Between the lower endof the liquid separator 2 and the lower end of the evaporator 1 there isconnected a check valve 7 preventing gas and the condensate formedduring hot gas defrosting from flowing in an uncontrolled manner backthrough the supply conduit from the liquid separator 2. From a place inthe supply conduit between the check valve 7 and the lower end of theevaporator 1 a conduit 13 leads to the liquid separator 2. The conduit13, which contains a schematically indicated throttle means 11, servesto drain the evaporator 1 for liquid in order to maintain a sufficientdefrosting pressure and provide pressure equalization between theevaporator and the liquid separator 2 when the hot gas supply is shutoff.

In the return conduit 8 from the evaporator 1 through the liquidseparator 2 to the compressor 3 there is connected a valve 9 accordingto the invention. This valve normally keeps the return conduit 8 to thecompressor open. However, upon opening of a solenoid valve 10 hot gasfrom the pressure side of the compressor 3 may be supplied to the valve9 in order to close or shut off the return conduit 8 and inject hot gasinto the evaporator 1 in the opposite direction.

The valve 9 is further shown in FIG. 2. As illustrated the valvecomprises a valve housing 12 having an inlet 14 and an outlet 16, avalve seat 18 and a flange 20 for connection with a cylinder housing 22having an opening 24 for the connection of a gas conduit.

Between the valve housing 12 and the cylinder housing 22 there isclamped a cup-shaped guide 26 for a valve stem 28. The guide 26 furtherseparates the interior 30 of the cylinder housing 22 from the flowpassage 32 between the inlet 14 and the outlet 16. Finally the guide 26constitutes an abutment for a helical spring 34, which acts on a piston36. A pressure equalization passage 38 is provided in the wall of theguide 26. The piston 36 is mounted on the valve stem 28 for restrictedmovement between a shoulder 41 and the lower end of a cap 40, which issecured at the outer end of the valve stem 28 between a shoulder and alocking ring 42. The cap 40 forms an annular chamber 44 whichcommunicates with the interior of the hollow valve stem 28 throughopenings 46 therein. In the cap 40 there is a throttle passage 47, thefunction of which will be discussed later.

At the end of the valve stem 28 opposite the cylinder chamber 30 thevalve stem carries a valve head 48 comprising a sealing ring 50 clampedbetween two disks 52, 54, which are secured in place by a nut 56 and alocking plate which is not illustrated. The design of the valve headprovides for automatic centering in the valve seat 18, and the taperingshape prevents radial extrusion of the sealing ring 50.

On the periphery of the valve stem 28 there is milled an axial groove 58which provides pressure relief between the cylinder chamber 30 and theflow passage 32 shortly before the valve head 48 engages the valve seat18. Finally, a throttle passage 60 may be provided in the valve stem 28,the function of which will be discussed later.

When the main flow passage 32 from the inlet 14 to the outlet 16 is tobe closed and a fluid injected in the inlet 14 for flow in the oppositedirection of the main fluid flow, the injection fluid will be suppliedthrough the opening 24. Provided that the pressure of the injectionfluid is sufficiently high to overcome the force of the spring 34 andthe pressure in the cylinder chamber 30, the valve stem 28 will move tothe left towards the valve seat 18. The spring force will keep thepiston 36 in engagement with the cap 40, the area of the annular chamber44 being so dimensioned that the positive pressure force exceeds theforces of inertia on the valve stem 28 during acceleration towards thevalve seat 18. The piston 36 and the valve stem 28 will thus move withthe same speed towards the valve seat 18.

The passage 38 is so dimensioned that the gas in the cylinder chamber 30will be slightly compressed. The purpose thereof is to reduce the speedwith which the valve stem 28 is moved, so that the impact against thevalve seat 18 is damped. Shortly before the valve head 48 engages thevalve seat 18, the groove 58 has arrived in such a position that thecompressed gas in the cylinder chamber 30 is released, see FIG. 3, sothat the pressure is approximately equalized in the moment when thevalve head engages the valve seat. The full sealing pressure istherefore obtained immediately.

When the valve head 48 and thus the valve stem 28 engages the valve seat18 and thereby comes to a halt, the piston 36 will continue to theposition shown in FIG. 4. Thereby the openings 46 are exposed, and theinjection gas is admitted into the inlet 14 through the hollow valvestem 28. The pressure on the piston 36 will now drop rapidly dependingon the pressure of the injection fluid, the flow rate and the height Xof the annular gap 45 leading into the annular chamber 44. When thepressure in the inlet 14 is the same as the pressure in the outlet 16 atthe moment when the valve head 48 closes the passage 32, a condition forthe valve to stay closed is that there is a certain pressure lossthrough the annular gap 45. If the inlet 14 is associated with a verysmall volume, it is not necessary to rely on a pressure drop across theannular gap. In such a case the height X is designed so that the annulargap 45 provides the same area as the sum of the openings 46. Even if theflow rate is 0, the valve will stay closed, provided that the areas andpressure differences of the movable parts provide a larger pressureforce than the spring force. In this respect the difference in areabetween the piston 36 and the valve seat 18 is an important factor.

In practice the space into which the fluid is injected through the inlet14, has a certain volume, and there will also be a certain flow leavingthis volume. The height X must therefore be adjusted to the actualsituation. For the rest, the valve will provide for a certain pressuredifference between the pressure of the injection fluid and thereby therecipient (evaporator) on the one hand and the pressure in the outlet 16and the main flow passage 32 on the other hand, the piston 36 movingback towards the cap 40 if the pressure difference across the piston 36becomes too low. The piston 36 returns to the shoulder 41 when thepressure difference is again sufficiently high.

When the valve 9 is again to be opened upon completion of the injection,it will usually be sufficient simply to close the valve 10 so that theflow of injection fluid is shut off. The reason therefor is that a flowleaving the volume with which the inlet 14 is associated, will reducethe pressure in the system. After a relatively short time the springforce is larger than the pressure forces keeping the valve shut, and thespring 34 will therefore move the piston 36 and the valve stem 28 backinto the starting position. When the piston 36 has engaged the cap 40and the annular gap 45 is thus closed, the passage 47 will equalize thepressures. Additionally, there will usually be small leakages along thesurface with which the piston 36 engages the cap 40, which will providea sufficiently fast return movement.

If there is no flow from the volume into which the fluid is injectedthrough the inlet 14, it is possible to equalize the pressure through apassage to the outlet 16 from the chamber on the right side of thepiston 36 or from the inlet 14. Such a passage can be mechanicallycontrolled by a shut-off valve. Alternatively, the passage may beprovided by the throttle passage 60 provided that loss of injectionfluid in the injection phase is acceptable.

It will be seen that the valve according to the invention acts both as ashut-off valve and as an injection valve, the shut-off function beingfirst provided by means of the pressure of the injection fluid,whereupon the injection fluid will flow through the valve and beinjected at the inlet side of the closed main flow passage.

What is claimed is:
 1. A valve for shutting off or closing a main fluidflow through a main flow passage (32), comprising a valve stem (28)having a valve head (48) which may be operated to engage a valve seat(18) in order to close said passage, the valve stem carrying at the endremote from the valve head a piston (36) which operates in a cylinder(22) and can be actuated by a closing fluid against spring action inorder to move the valve stem (28) and the valve head (48) into closedposition, characterized in that the valve stem (28) is hollow and at theend at which the valve head (48) is provided, is open and at theopposite end has openings (46) opening into the interior of the hollowvalve stem (28), and that the piston (36) is mounted for axial movementon the valve stem (28) to allow further movement towards the valve seat(18) against spring action when the valve head (48) has engaged thevalve seat (18) and the valve stem (28) has therefore come to a halt,said further movement relative to the valve stem (28) opening a passage(45) into the openings (46) in the valve stem (28), whereby closingfluid will be injected into the main flow passage (32) at one side ofthe valve seat (18) through the valve stem.
 2. A valve according toclaim 1, characterized in that the cylinder chamber (30) on the side ofthe piston (36) not subjected to the closing and injection fluid,communicates with the main flow passage (32) through throttle passages(38) and is thus filled with the main fluid, which is compressed duringthe closing operation to provide a braking and damping effect on theclosing movement of the valve stem.
 3. A valve according to claim 2,characterized in that there is provided a relief passage (58) whichimmediately prior to the valve head (48) engaging the valve seat (18) isopened to provide rapid equalizing of the pressure difference betweensaid cylinder chamber (30) and the main flow passage (32).
 4. A valveaccording to any one of claims 1, 2 or 3 characterized in that there isprovided a throttle passage (47, 60) from the cylinder chamber subjectedto the closing and injection fluid pressure, to the other side of thevalve seat (18) to relieve the pressure when the closing and injectionfluid supply is closed, whereby the valve will be returned to openposition by the spring force acting on the piston (36).